This invention concerns tapping tooling adapted to be mounted in a press and driven by the press motion to carry out a tapping of punched bores in a workpiece.
Such devices have been used to eliminate separately conducted tapping steps.
U.S. Pat. No. 5,173,015 discloses a device in which the press motion drives a shallow pitch planetary roller unit to directly drive a tap to be rotated and advanced axially to carry out a tapping operation.
In other designs, a more steeply pitched ball screw is driven by the press, and a complicated multistage gear train used to rotate the tap at the proper rate of rotation.
See U.S. Pat. Nos. 5,348,429 and 4,692,072 for examples of these devices.
In some prior designs, a steep pitch ball screw is used alone, see U.S. Pat. No. 2,314,138. However, in modem high speed stamping operations, the tap must be rotated more quickly than can be achieved directly by a ball screw mechanism, necessitating the use of the expensive planetary roller nut described alone.
In addition, a change in the tap pitch requires a replacement of the ball screw.
Very shallow pitch threads create high loadings, and add on cam units have been employed to reduce shock loadings for shallow pitch roller nut designs.
In addition, shallow pitch threads are prone to self locking jams.
Another disadvantage of prior designs is the difficulty in changing tap sizes, requiring time consuming changes of the tap holder and/or tap.
It is the object of the present invention to provide an in die tapping unit which is simpler and does not require multistage gearing or very shallowly pitched planetary roller nut devices, and avoids high shock loadings or self locking jams.
It is another object of the present invention to provide such an in-die tapping tool which easily allows changes in tap sizes and replacement of the taps themselves.
These and other objects which will become apparent upon a reading of the following specification and claims are achieved by a tapping unit having a pair of ball screw mechanisms each having a ball screw shaft of intermediate pitch, each rotated by the advance of respective ball nut by the press platen.
A single stage gear drive is arranged between each ball screw shaft and a central gear hub which receives a rotatable pitch adapter sleeve rotated therewith. The rotatable pitch adapter sleeve has an external thread matched to the tap pitch received in a threaded bore in a surrounding fixed pitch adapter hub.
A tap holder is carried within the rotating pitch adapter sleeve and advances axially therewith when the gear hub is rotated. A quick release coupling secures a tap in the tap holder, and the tap holder may be lifted from the pitch adapter to be changed.
The tap holder is held in the pitch adapter with a snap ring and keyed thereto to rotate therewith.
An upper housing piece carrying the ball screw nuts and a lower housing piece carrying the pitch adapter components are held together by a pair of interposed gas springs, which together with surrounding return springs resist movement of the upper housing piece relative the lower housing piece. A striker pad is slidable in a bore formed into the top.of the upper housing piece with an interposed spring resisting movement into the bore. The spring stiffness is set so that the upper housing is accelerated to the ram speed prior to the ram contacting the top surface of the upper housing piece. This reduces the shock loading of the ball screw and other components.
The use of two ball screws and single stage gear train driving pitch adapter components to rotate and axially advance a top holder simplifies the unit and also reduces the shock loading to increase the load capacity of the tool, as well as service life and cycle rate.
The single stage gearing allows for use of more commonly available right hand helix lead screws.
Also, the single stage gearing can be readily changed to match the axial advance and rotation to a particular tap pitch.
The tap holder can also be readily removed from a movable pitch adapter sleeve to accommodate a change in tap size.